Define new 'bandwidth' element with possible child element 'inbound'
and 'outbound' addressing incoming and outgoing traffic respectively:
<bandwidth>
<inbound average='1000' peak='2000' burst='5120'/>
<outbound average='500'/>
</bandwidth>
Leaving any element out means not to shape traffic in that
direction.
The units for average and peak (rate) are in kilobytes per second,
for burst (size) are just in kilobytes.
This element can be inserted into domain's 'interface' and
'network'.
virtPortProfiles are currently only used in the domain XML, but will
soon also be used in the network XML. To prepare for that change, this
patch moves the structure definition into util/network.h and the parse
and format functions into util/network.c (I decided that this was a
better choice than macvtap.h/c for something that needed to always be
available on all platforms).
